I have a 2001 Subaru but bought in (Sept. 2000) , it's an automatic, Basic L version.. For the past year I've had the check engine light on.. I've had driviblitity issues where the car sometimes seems to stall, but you hear this popping sound.. My mechanic was able to get it off to pass inspection however we tried within a year to fix it.. I've replaced sensors out the wazoo and have spent probably over $2000 trying and so for nothing.. The sensors that were replaced were brand new sensors and when the mechanic tested again the codes would come back and say "bad sensors" when they weren't.. I've even called Subaru to see if my car was on list of the recalls in Year 2000 for a system update, they keep saying "NO".. The only thing my mechanic is thinking of is that performing a "smoke" test to see where this air leak is in hoses or wires.. What do you think ?? Any other ideas ?? .. However I seem to get the drivablilty popping issue when it gets colder outside and or raining so I don't know if that has anything to do with it.. I've never had a problem this bad , and from what I've hearing that Subaru cars are suppose to last a good time.. Well any other suggestions or opinions would be great..
Thanks,
Dxtra
P. S. - And "NO" I can not afford a new car... LOL

I don't know off by hand I'd have to ask the mechanic again.. When I've been there he said he was "puzzled" as to why the codes would come up bad sensor.. He would clear the codes and check engine light would go away, but again after 10 minutes of driving the check engine light comes right back on..

For those who haven't read this on other posts: Most AutoZone stores will read your code for free. I've had a constant Check Engine light lit the past couple of days so I took it to AutoZone and they diagnosed the problem as a knock sensor malfunction within minutes and handed me a full printed report for free. What you do with their advice is up to you but at least you know what your car is trying to tell you. Oh, I'm in Lawrence, KS.

I am getting that p0420 code myself. Many times its the gas cap that is the problem. I just haven't had the time to really check it out yet. I would check out what sensor is involved and look in between. If the ECU is not getting a signal, well it flags it and throws a CEL. The sensor could be good after all.

I've replaced the gas cap on my 1st try and that wasn't it.. All the sensors I got were tested and all are in good if not great conditon... Thanks for the suggestion tho..

For those who haven't read this on other posts: Most AutoZone stores will read your code for free. I've had a constant Check Engine light lit the past couple of days so I took it to AutoZone and they diagnosed the problem as a knock sensor malfunction within minutes and handed me a full printed report for free. What you do with their advice is up to you but at least you know what your car is trying to tell you. Oh, I'm in Lawrence, KS.

Like i said in above posts, I've already replaced the Knock sensor with a new one .. I don't think Autozone will tell me anything different then my mechanic did but if it's free I guess I should try it.. Thanks!

Was the front & rear O2 sensors replaced? Other then the CEL, does your '01 seem to be operating normally?

IMO, a failing "front" O2 (A/F, air/fuel) sensor will cause hesitation, back fire & sooty exhaust pipe (running rich). The rear O2 sensor is used to monitor the operation of the CAT. It won't cause your engine to operate poorly. It does tell you (CEL code P0420) if the CAT is going south, or something further upstream is not right.

I had the same problem and seen the problem quite a few times on other subies. If the O2 sensors didn't fix it, the next step was a cat. i have used the one from autopartswarehouse.com a couple times with no issues. I have been running mine for 2 years and it is still good. Haven't had any customers cars with issues either. Much less expensive than a factory cat from the dealer.

[QUOTE=SHOguy;385440]If the O2 sensors didn't fix it, the next step was a cat.

My 99 Forester would code for a faulty cat. I'd clear the code and it would come back. The dealers wanted to replace both cats and/or O2 sensors. I was using some oil (1qt/1000mi). The car had 150K miles. When the engine went south (spun crank bearings) I found that all 8 exhaust valves were loosing oil through the guides. Since I did the rebuild I've had no codes so my theory is the CATS and stream sensors could not threshold the polluted air I was feeding them hence the coding. If the car is old and worn I'd look to engine components for failure.